Passing null parameters to x:Bind function binding

I'm trying to bind an object using x:Bind function binding. See https://docs.microsoft.com/en-us/windows/uwp/data-binding/function-bindings.

This works fine as long as the parameter has a value. But if the parameter is null, the function is not called and the binding uses FallbackValue instead (if it is defined).

<TextBlock Text="{x:Bind local:MainViewModel.FormatWidget(ViewModel.SelectedItem), Mode=OneWay, FallbackValue=MyFallbackValue}" /> 

Interestingly, if the initial value is null, x:Bind does call the function with the null parameter, but on any subsequent changes when the parameter becomes null, the function is not called. It is for this one reason that I would call this a bug rather than a feature request. Surely this is not the intended behavior.

Please fix x:Bind to accept null parameters.

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